DiningPhilosophers.scala

import scala.util.Random
import java.util.concurrent.locks.ReentrantLock

def dinner(number: Int, delayInMs: Int = 10) =
  
  val forks = Array.fill(number)(new ReentrantLock)

  // warning: running each philosopher in their own explicit Java thread
  def phil(i: Int) = new Thread:
    override def run(): Unit =
      val leftFork = forks(i)
      val rightFork = forks((i + 1) % number)
      while true do
        println(f"$i thinking")
        Thread.sleep(Random.nextInt(delayInMs))
        println(f"$i hungry, waiting for left fork $i")
        leftFork.lock()
        Thread.sleep(1)
        println(f"$i got left, now waiting for right fork ${((i + 1) % number)}")
        rightFork.lock()
        // ^^^ comment out if using tryLock
        // if rightFork.tryLock() then
        println(f"$i eating")
        Thread.sleep(Random.nextInt(delayInMs))
        rightFork.unlock()
        // end if
        leftFork.unlock()
      end while
    end run

  (0 until number).foreach(n => phil(n).start())
end dinner